Structural Analysis and Inclusion Mechanism of Native and Permethylated α‐Cyclodextrin‐Based Rotaxanes Containing Alkylene Axles

Native α‐cyclodextrin‐ (α‐CD) and permethylated α‐CD (PMeCD)‐based rotaxanes with various short alkylene chains as axles can be synthesized through a urea end‐capping method. Native α‐CD tends to form [3]‐ or [5]pseudorotaxanes and not [2]‐ or [4]pseudorotaxanes, which indicates that the coupled CDs act as a single fragment. End‐capping reactions of the pseudorotaxanes with C18 and C24 axle lengths do not occur because the axle termini are covered by the densely stacked CDs. The number of PMeCDs on the pseudorotaxane is flexible and mainly depends on the axle length. Peracetylated α‐CD (PAcCD)‐based rotaxanes are synthesized through O‐acetylation of the α‐CD‐based rotaxanes without any decomposition of the rotaxanated structures. The structures of PMeCD‐based [3]‐ and [4]rotaxanes, and the molecular dynamics calculations on [3]pseudorotaxanes, indicate that the tail face of PMeCDs is regularly directed toward the axle termini. On the basis of the results obtained, it can be concluded that the directions and numbers of CDs in rotaxanes containing short alkylene chains depend on 1) the interactions between CDs, 2) the length of the alkylene axle, and 3) the interactions between the axle end and tail face of the CD.     

Dissociative adsorption of hydrogen on the ZrB2(0001) surface

We have studied the dissociation of H₂ on the ZrB₂(0001) surface using density functional theory and reflection absorption infrared spectroscopy (RAIRS). Our results show that H₂ readily dissociates on the Zr-terminated (0001) surface up to a H coverage of 1/2 ML. Furthermore, we show that H is very mobile on the surface and that it desorbs between 545 and 625 K. The calculated vibrational frequencies for the adsorbed H are in excellent agreement with our RAIRS measurements and with previously reported high resolution electron energy loss spectra.     

Quantitative and in situ Detection of Oxidatively Generated DNA Damage 8,5′‐Cyclo‐2′‐Deoxyadenosine Using an Immunoassay with a Novel Monoclonal Antibody

Xeroderma pigmentosum (XP) is a genetic disorder associated with defects in nucleotide excision repair, which eliminates a wide variety of helix‐distorting types of DNA damage including sunlight‐induced pyrimidine dimers. In addition to skin disease, approximately 30% of XP patients develop progressive neurological disease, which has been hypothesized to be associated with the accumulation of a particular type of oxidatively generated DNA damage called purine 8,5′‐cyclo‐2′‐deoxynucleosides (purine cyclonucleosides). However, there are no currently available methods to detect purine cyclonucleosides in DNA without the need for DNA hydrolysis. In this study, we generated a novel monoclonal antibody (CdA‐1) specific for purine cyclonucleosides in single‐stranded DNA that recognizes 8,5′‐cyclo‐2′‐deoxyadenosine (cyclo‐dA). An immunoassay using CdA‐1 revealed a linear dose response between known amounts of cyclo‐dA in oligonucleotides and the antibody binding to them. The quantitative immunoassay revealed that treatment with Fenton‐type reagents (CuCl₂/H₂O₂/ascorbate) efficiently produces cyclo‐dA in DNA in a dose‐dependent manner. Moreover, immunofluorescent analysis using CdA‐1 enabled the visualization of cyclo‐dA in human osteosarcoma cells, which had been transfected with oligonucleotides containing cyclo‐dA. Thus, the CdA‐1 antibody is a valuable tool for the detection and quantification of cyclo‐dA in DNA, and may be useful for characterizing the mechanism(s) underlying the development of XP neurological disease.     

Rational Synthesis of Antiaromatic 5,15‐Dioxaporphyrin and Oxidation into β,β‐Linked Dimers

5,15‐Dioxaporphyrin was synthesized for the first time by a nucleophilic aromatic substitution reaction of a nickel bis(α,α′‐dibromodipyrrin) complex with benzaldoxime, followed by an intramolecular annulation of the α‐hydroxy‐substituted intermediate. This unprecedented molecule is a 20π‐electron antiaromatic system, in terms of Hückel's rule of aromaticity, because lone pair electrons of oxygen atoms are incorporated into the 18π‐electron conjugated system of the porphyrin. A theoretical analysis based on the gauge‐including magnetically induced current method confirmed its antiaromaticity and a dominant inner ring pathway for the ring current. The unique reactivity of 5,15‐dioxaporphyrin forming a β,β‐linked dimer upon oxidation was also revealed.     

Poecillastrin E,F, and G,cytotoxic chondropsin-type macrolides from a marine sponge Poecillastra sp.

Poecillastrin E (1), F (2), and G (3) were isolated from a marine sponge Poecillastra sp. as the cytotoxic constituents. Their planar structures were determined by analyzing the MS and NMR spectra. They are closely related to the known poecillastrin C (4). The absolute configuration of the β-hydroxyaspartic acid (OHAsp) residue was determined to be D-threo by Marfey's analysis of the hydrolysate. The mode of lactone ring formation of OHAsp residue in 1–3 was determined by selective reduction of the ester linkage followed by acid hydrolysis.